FutureWarning raised by `browser.cookies.delete()`

[jace]

trafficstars

Pytest-Splinter's browser fixture deletes cookies by calling browser.cookies.delete():

https://github.com/pytest-dev/pytest-splinter/blob/47141cd477254abcb2a15cdf7e72bdb97da29f95/pytest_splinter/plugin.py#L609-L615

This is causing a FutureWarning under splinter 0.19:

…/splinter/driver/webdriver/cookie_manager.py:24: FutureWarning: Deleting all cookies via CookieManager.delete() with no arguments has been deprecated. use CookieManager.delete_all().

Splinter's documentation has been updated to recommend calling delete_all(): https://splinter.readthedocs.io/en/latest/cookies.html#delete-all-cookies

[jace]

I missed the existing open PR in #172.